1. Field of the Invention
The present invention relates generally to a bicycle crank arm, and in particular to a method for readily and efficiently manufacturing a one-piece crank arm and spider assembly having enhanced surface appearance.
2. The Related Art
Being lightweight is one of the most important concerns in the bicycle industry. A number of bicycle parts are made hollow for reducing the overall weight of the bicycle. This is true of bicycle crank arm as well. Bicycle crank arms having a hollow body are known. However, the manufacturing process for such hollow crank arms is complicated, making it difficult and expensive to manufacture the crank arms. In addition, a spider that holds a sprocket must be mounted to the crank arm in a separate process by riveting or other known techniques after the manufacturing of the crank arm. Thus, the manufacturing time is substantially increased and the overall strength of the crank arm is adversely affected.
Further, the crank arms made by the conventional process may have a bad looking appearance. This makes the final product of bicycle not appealing to the general consumers.
It is thus desired to have a method for manufacturing bicycle crank arms without the above noted drawbacks.